The statements in this section provide background information related to this disclosure and may not constitute prior art.
Heat transfer devices that operate using a vapor-compression refrigeration cycle, including heat pumps, air conditioners (including auto, home, and industrial air conditioners), and refrigerators (including home and industrial refrigerators and freezers), employ refrigerants and lubricants during operation. In a typical heat transfer system, a liquid of suitable boiling point evaporates at low pressure, absorbing heat in doing so. The vapor produced is then compressed and passed to a condenser where it is condensed, generating heat. The liquid condensate is returned through an expansion valve to the evaporator, completing a refrigeration cycle. One important type of refrigeration system is known as “small refrigeration” or “domestic refrigeration” systems, which encompasses systems that are typically used in residential homes, apartments and the like for consumer use in refrigerators, freezers, and the like. Also frequently included in this group are vending machines and the like. Another important refrigeration system comprises automotive air conditioning systems used to provide cooling in motor vehicles.
Refrigerants are often combined with compatible lubricants to form the refrigeration liquids used in the refrigeration compressors. The lubricants ensure that moving parts of the heat transfer devices are lubricated to facilitate operation and avoid wear. Government regulations have affected which fluids may be used as refrigerants in these devices. This in turn has necessitated finding new lubricants that will work well with the new refrigerants. Devices are generally designed to use lubricants that are miscible with the refrigerant during operation. To perform as a satisfactory refrigeration liquid, the mixture of refrigerant and lubricant must be compatible and miscible over a wide temperature range.